Machine for extruding rubber and the like



Malrch 7, 1944. RE, BROWN 2,343,529

MACHINE FOR EXTRUDING RUBBER AND THE LIKE Filed July 18, 1941 Y '4 SheetsSheet 1 VE/WOERI FE BROWN March 7, 1944. 5, BROWN 2,343,529

MACHINE FOR EXTRUDING RUBBER AND THE LIKE I Filed July 18, 1941 4 Sheets-Sheet wwmroe F. E .BRQWN F. E. BROWN I 2,343,529

MACHINE FOR EXTHUDING RUBBER AND THE LIKE Filed July 18, 1941 4 Sheets-Sheet 5 March 7, 1944i I wry/me F. E .BROW N March 7, 1944- F. E. BROWN 2,343,529

MACHINE FOR EXTRUDING RUBBER AND THE LIKE Filed July 18, 1941 I 4 Sheets-Sheet 4 Fig 4. 4

197' TOR/V! V5 of an extruding machine in which the materialis fed to the die by means of the scroll can be Patented Mar. 7, 1944 UNITED STATES: PATENT orrlca Frederick Edward Brown, Hyde, time Application July 18, 1941, $erial No. 403,041 In Great Britain November 9, 1939 8 Clairgs. (Cl. 18-12) This invention relates to machines for extruding rubber and the like and to feed scrolls for use The emciency of such machines is low. This eni-v ciency is measured as the ratio between the amount of material which is extruded per unit length of time and the volume swept out by one complete turn of the scroll in that time, and is generally of the order of 33% for rubber and 25% for dead" material like ebonite. The provision of a feed roll which forces the material into the scroll at the feed end increases the efliciency tosome extent and can, indeed, raise the efliciency when rubber is being extruded toas much as 40%; The provision of such a feed roller however is a complication which it is desirable to avoid because of the difficulty of providing adequate bearings in the very limited space which is available.

There is thus a good deal of room for improvement particularly when it is considered that the eificiency is constantly being decreased'as wear of the scroll or of the casing which surrounds it, takes place. A test carried out on a machine of modern design still in use shows that the output capacity had been reduced by as a result of wear of the scroll.

The applicant has now found that the efliciency quite substantially increased if the scroll has more threads at the delivery end than at the feed end, the volumetric capacity per unit length or the scroll being roughly constant over its whole ,bination of these three factors.

length. Best results have been obtained when the scroll has :been tapered towards the delivery end and the scroll has had a single thread at the feed end, two threads over its intermediate portion ,and three threads at the delivery end. With such a scroll, an efllciency of without the use of a feed roller has been obtained when e x-,

trading rubber.

The tapering of the scroll has an important bearing on the 'emciency of the machine and also provides a simple method of adjusting the parts ,Thlll,

of the machine so as to compensate for wear. it the casing which, of course, is internally tapered. is mounted for axial adjustment relatively to the scroll, wear simple expedient of moving the easing into closer contact with the scroll. siderable importance.

The provision of a tapered scroll is also important from another aspect. In general, the die opening through which the material is extruded will be smaller than the end of the scroll. A sudden change in diameter at the delivery end will result in high pressure being exerted on the die gear without producing any correspondingly large increase of pressure on the material passing through the die opening. The reduction in diameter of the scroll at the delivery end allows the material to be fed more directly towards the die opening, and makes it feasible in most cases to taper the bore of the casing continuously from the end of the scroll to the die so that this part of the casing does not unduly oppose the forward movement of the material to the die.

In the ideal case, the volumetric capacity of the scroll would be the same at all-points along it. With a continuously tapered scroll this would mean continuous alteration along the length of the scroll either of thepitch of the groove or grooves, or the width or the depth or of any com- There are, however, practical limits to the magnitude of the pitch, the width and the depth of they groove and in practice it is found that a sufficiently good approximation to the ideal can be obtained by dividing the scroll up keeping the pitch constant over each length and the cross-section of the groove constant throughout the length of the scroll.

Where, as is the case in th preferred form of the invention, the scroll is tapered and the crosssection of the groove is made constant throughout diameter of the scroll greater than is the length of the scroll, the at the feed end has to be made because it .ensures a more positive feed intake 01' the material to hated by thescroll.

In order that the invention may be properly understood and be morereadily carried into eflect, two examples oi machines in accordance ith the invention will now be described with eference to the accompanying drawings, in which- Figure 1 is a longitudinal section through one form of extruding machine in accordance with the invention;

Figure 2is a plan view of Fi ure l;

Figure 3 is a cross-section taken on the line Ill-III in Figure 1; and

can be taken up by the This-is a feature of 0011-,

into three lengths and Figure 4 is a longitudinal section compondin to that shown in Figure 1 through a machine having a diii'erent feed scroll.

Themachineshowninl'igureslto3hasa base It on which is fixed a casing 4 which surrounds and fits a feed scroll I. The scroll I is axially fixed and is mounted for rotation in a width throughout the length of the scroll.

The rear portion 8 of the fixed casing is Drovided with a feed hole or passage II which is tangential to the rear end oi the scroll. The material to be extruded is fed through thk feed hole and is moved towards the delivery end by the combined veii'ect of the slope of the thread is and the friction between it andthe casing.

At the end of the casing 4- beyond the'delivery end of the scroll an internally screw-threaded ring I! is provided which receives an appropriately screw-threaded-extruding die It. The material which'is delivered from the end of the scroll is forced through this die and emerges as a continuous rod, strip or tube of a cross-section determined by the shape of the die.

It has been found that the volumetric efliciency of such amachine is quite substantially higher than that of the normal extruding machine which has a scroll which is parallel throughout its length and a groove of constant pitch. The full reasons for this important improvement are not fully understood but that the improvement exists is quite certain.

Constant use of the machine produces wear of the scroll and of the fixed casing which surrounds it. In the machine shown here provision is made for taking up this wear. It will be seen that the rear part of the casing is fixed to the bed plate II by means of screws it which pass through elongated holes 22. bed plate," has a pair of lugs 23 at the front through which pass adjusting screws 24. These screws abut against a part 25 of the casing. If then, as a result of wear, the clearance between the scroll and the tapered part i of the casing becomes unduly, large, it is mereiy necessary to loosen'the screws ii and tighten the screws 24 so that the casing'is moved backwards relatively to the scroll. The casing is then secured to the base 20 in its adjusted position by re-tightening the screws 2i and adjusting the lock-nuts Na on the screws 24. This very simple provision is of the greatest importance as it allows the elliciency of the machine to be maintained over a long period.

The essential parts of the machine shown in Figure 4 correspond to those of the machine described above. The machine shown here has, however, a different form of scroll 2. The rear end t of the scroll is again parallel and the for ward end I is continuously tapered to the delivery end. Over the parallel portion, the scroll, as before, has a single thread iii. This extends over the whole of the length A which includes a part of the tapered portion of the scroll. Over the intermediate length B the scroll has a double thread I ll, Ila, and over the portion '0 at the delivery end it has three threads ll, Ila, llb.

It will also be seen that the assasao The groove II is of the same cross-section everywhere except at the junction of the lengths A, B and B, C. The casing I diners from that shown in Fig- .l ure 1 in that it is made in one piece, but it is provided with the same kind of adjusting means as are shown in Figure 1.

The ring is which connects the die It to the casinghas a tapered portion 2 forming a conl tinuous extension of the bore of the casing. This is quite important because it ensures that there is no sudden diminution in diameter or the passage through which the material has to pass on the way to the die. There is then no undue opposition to the delivery of the material.

This form of scrollgives a somewhat better efllciency than that shown in Figure 1. The multiple thread at the delivery end of the scroll causes the material to be delivered from the scroll to the die from a number of points round the scroll simultaneously. This has the important advantage of equalising pressure at all points within the die and of consequently leading to the production of an extruded article having 25 no local blemishes or faults.

If desired, a feed roller can be provided to give a more positive feeding action at the feed end of the scroll but, in general, this is not necessary.

The efllciency of the machine shown here in which so no such feed rolls are provided is higher than that oi the standard machine provided with a feed roll.

Neither of'the two scrolls illustrated and de scribed here is of strictly constant volumetric capacity at all points along its length. The volumetric capacity is, however roughly constant so I that there is no great tendency towards important variations in the volumetric rate of feed at diii'erent points along the scroll.

Iclaim:

1. An extruding machine for rubber and like material comprising a casing and a feed scroll within and coacting with said casing said feed scroll having at least one more thread along a part or its length adjacent its delivery en than along theremainder of its length, the volumetric capacity of the scroll being substantiall the same at all points along its length, and said casing having an open end at the delivery end of the n scroll said open end constituting the sole outlet for extruded material.

2. An extruding machine for rubber and like material comprising a casing and a feed scroll within and coacting with ,said casing said feed scroll having at least one more thread along a :5 part of its length adiacent its delivery end than along the remainder of its 'length and said threads defining grooves of substantially the same cross-section throughout the length of the scroll.

3. An extruding machine for rubber and like material comprising a casing and a feed scroll within and coacting with said casing said teed scroll having at least one more thread along a part of its length adjacent its delivery end than along the remainder of its length and said casing having an open end at the delivery end or the scrool said open end constituting the sole outlet for extruded material, the scroll having a parallel portion adjacent the feed end and a tapered portion adjacent the delivery end and at least one more thread on its tapered portion than on its parallel portion, the said threads defining grooves of substantially the same cross section throughout the length of the scroll.

4. An extruding machine for rubber and like threads defining grooves or substantially the.

material comprising a casing and a reed scroll within and coacting with said casing said feed scroll having at least one more thread along a part of its length adjacent its delivery'end than. along the remainder of its length and said casing having an open end at the delivery end oi. the scroll said open end constituting the sole outlet for extruded material, said feed scroll tapering towards the delivery end over the greater part or its length and having at least one more thread on a portion thereoi. adjacent its delivery end than on the remainder thereof, the said threads defining grooves of substantially the same cross section throughout the length of the scroll.

5. An extruding machine tor rubber and like material comprising a casing and 'a, feed scroll within and coacting with said casing said teed scrool having at least one more thread'along a part or its length adjacent its delivery end than 4 along the remainder of its length and said casing i having an open end at the delivery end or the scroll said open end constituting thelsole outlet tor extruded material, the scroll having a parallel portion adjacent the feed end and having a single thread and a tapered portion adjacent'the delivery end having two threads, the said same cross-section throughout thelength oi. the scroll.

' 6. An extruding machine as set forth in claim 2- in which the scroll has a parallel portion adjacent the feed end and a tapered. portion adjacent the delivery end and has at least one more thread on its tapered portion than on its parallel portion, the said threads defining grooves of substantially the same cross-section throughout the length of the scroll.

7. An extruding machine as set forth in claim 2 in which said teed scroll tapers towards the delivery end over the greater part of its length and has at least one more thread on a portion thereof adjacent its delivery end than on the remainder thereof, the said threads defining grooves of substantially the same cross-section throughout the length of the scroll.

' 8. An extruding machine as set forth in claim 2 in which the scroll has a parallel portion adjacent the feed end having a single thread and a tapered portion adjacent the delivery end having two threads, the said threads defining grooves oi substantially the ame cross-section throughout the length or the scroll.

FREDERICK EDWARD BROWN. 

